brainpopfandomcom-20200223-history
Relative Dating/Transcript
Transcript Text reads: The Mysteries of Life with Cassie and Moby An animation shows a long table with robots seated around it. The bots are playing the Happy Birthday Song on kazoos. A girl, Cassie, sits at the end. She is drinking orange juice as a very large cake with candles is wheeled toward her. CASSIE: 13-layer cake—my favorite! Cassie takes a big breath to blow out the candles. MOBY: Beep! CASSIE: Gahh! Cassie’s robot friend, Moby, pops out of the cake. Cake has splattered all over Cassie’s face, as well as all the other robot guests. Moby smiles and plays the “and many more” line of the Happy Birthday Song on kazoo. Moby hands Cassie a letter. Cassie reads from the typed letter. CASSIE: Dear Cassie and Moby, How old is Earth? From, Delvis. CASSIE: That's a question people have been puzzling over for… maybe as long as there've been people! Up until pretty recently, it was thought that only religion could provide an answer. One common idea was that the whole universe gets destroyed and re-created in an endless cycle. An animation shows the Milky Way with arrows pointing in a cycle around it. CASSIE: According to Maya mythology, the last creation was a few thousand years ago. Hinduism said we’re billions of years into the latest cycle. The Milky Way image is shown twice on a timeline: once at a point labeled “3,000 years ago” and once at a point labeled “4 billion years ago.” CASSIE: In the Christian Bible, Earth and the universe were created just once, at some unknown point in the past. An animation shows a question mark over the timeline. CASSIE: Of course, no one could go back in time to find out what really happened. But a few centuries ago, scientists started to realize: Actually, we kind of can. An animation shows a man, Nicolaus Steno, using rope to climb down a steep cliff. MOBY: Beep? CASSIE: The key was rock layers, or strata, like these. In the 1600s, a scientist named Nicolaus Steno wondered how strata form. An animation shows some of the layers of rock present in the cliff. CASSIE: He reasoned that they’re made of sediments: bits of rock and other debris. They get picked up by water or wind, and dropped off somewhere else. An animation shows small pebbles getting picked up by the wind. CASSIE: Because of gravity, sediments settle in horizontal layers. Over time, these layers compress and harden into sedimentary rock. That means younger strata always form on top of older ones. An animation shows the pebbles gradually transition from widely spaced to very close together. CASSIE: Steno called this idea the principle of superposition. It let him identify one layer as older than another based on their positions. An animation shows Steno label the base of the cliff as “oldest.” Then he jumps up to the top of the cliff and labels it “youngest.” CASSIE: This kind of ordering is called relative dating. And it was the first step toward figuring out how old Earth is. MOBY: Beep? CASSIE: Well, each layer takes a certain amount of time to form. Figuring out that amount would be the first step to calculating Earth's age. An animation shows a section of rock. Each strata is labeled with a different-sized hourglass. CASSIE: In the 1700s, a geologist named James Hutton made some rough estimates. He noticed that after his farm flooded, the water left a thin layer of sediment. An animation shows Hutton standing on his farm with a calculator as it rains and then dries. CASSIE: He noticed that after his farm flooded, the water left a thin layer of sediment. And realized that sedimentary rocks form in razor-thin sheets. At that rate, it’d take many thousands of years to form a single layer of rock. An animation shows rock strata forming, layer by layer. CASSIE: Which seriously conflicted with what most Europeans thought: That Earth was a relatively young 6,000 years old… with big catastrophes like earthquakes and floods shaping its surface. An animation shows a man giving a speech at a podium. A speech bubble shows an image of Earth with big eyes and a tuft of hair, sucking on a bottle. CASSIE: Hutton’s idea was that Earth was much, much older. And that much of its surface was slowly shaped by ordinary processes. An animation shows Earth transform to an older planet with lots of wrinkles. MOBY: Beep? CASSIE: Hutton figured you could estimate Earth's age by adding up how long its different rock layers took to form. An animation shows Hutton looking at several sections of strata, holding a clipboard and writing notes. CASSIE: But you'd need to find layers from every part of the planet's history, all the way back to the beginning. Which seemed impossible. An animation shows the many layers of rock beneath the ground where Hutton is standing. CASSIE: First, strata at the surface were often a mess—folded, tilted, and eroded. An animation shows strata of different colors in a swirl instead of directly on top of each other. CASSIE: And it wasn’t always clear how layers in one place lined up with those in another. Scientists like Hutton needed a way to correlate them—to match up layers based on their age. An animation shows two images of strata from opposite ends of Europe. They look very different. MOBY: Beep? CASSIE: The first hint of a solution to this problem came from the underworld. William Smith was supervising the digging of coal mines in England. An animation shows a man, Smith, being lowered into a mineshaft with a rope. He holds up a lantern, illuminating the rock. CASSIE: He examined rocks for his work, but he was really interested in fossils: Traces of ancient living things that have been preserved. Smith comes across an ammonite fossil and holds his lantern up to look at it. CASSIE: In mine shafts across England, he noticed a pattern: Some kinds of fossils always showed up in layers above other kinds. Even all the way across the country, these fossils appeared in the same order. He wondered if similar strata in different places were actually connected. An animation shows a layer of strata with ammonite fossils on top of another layer of strata with trilobite fossils. A map shows that the same pattern exists in multiple locations. CASSIE: Luckily, Smith got an opportunity to find out—a gig supervising the digging of a canal. It would require slicing open long strips of land—perfect for testing his idea! An animation shows a video game-style miner digging from one section of the map to another. MOBY: Beep? WILLIAM SMITH: Yeah! CASSIE: Yep, just as he suspected, the layers with the same fossils were connected. This was a huge breakthrough. It meant you could easily correlate strata in separate places. If they had the same fossils, they must have formed around the same time. An image of a map shows the strata in northern Europe connected to the strata in northern Africa. CASSIE: Smith used the order of fossils to make the first large-scale geologic map. They show which rock layers are exposed at the surface. Different colors represent rocks of different ages and types. An animation shows a geologic map. The swirls of different colors represent different ages and types of rocks. CASSIE: Geologists began correlating and mapping strata all over the world. And that allowed for better estimates of Earth’s age. An image show the geologic map expanded to cover the entire world. CASSIE: In the 1800s, one geologist calculated that it's 96 million years old. Not many people embraced the idea at first. An animation shows a front-page newspaper headline that reads: “EARTH 96 M.Y.O.!” A man reads the newspaper with one eyebrow raised, then tosses the paper over his shoulder. CASSIE: But for the few who did, it changed everything. An extremely ancient Earth gave scientists an opportunity to think big. A young man catches the thrown-out newspaper and reads it with a smile on his face. Then he looks up and a lantern icon pops up over his head. CASSIE: Like Charles Darwin, who was studying changes across generations of organisms. And began to wonder what those differences might add up to over millions of years. The idea of an ancient Earth freed him to think about how life could change very, very gradually. An animation shows birds in a cage and the silhouette of an early human gradually forming into a modern-day man. CASSIE: We now know this concept as evolution, and it’s a guiding principle of biology. MOBY: Beep? CASSIE: The final piece of the puzzle came in the 1900s, with the invention of radiometric dating. It detects radiation levels in rocks to determine absolute age—how old they are in years. An animation shows a large machine labeled Dating Machine. A rock is dropped inside and the screen flashes “402 million years old.” CASSIE: Strata and relative age tells scientists where to find the oldest rocks. An animation shows the global geologic map. The oldest strata flash. CASSIE: And radiometric dating has given us a real number, in years. MOBY: Beep? CASSIE: Brace yourself—the latest evidence shows that Earth is more than four and a half billion years old! CASSIE: To help us wrap our minds around all that time, scientists use the geologic time scale. It organizes Earth’s history based on strata and the fossil record. An animation shows the geologic time scale. It looks similar to a timeline. The axis is labeled “billions of years ago.” From right-to-left, numbers count back from today to 4.6 billions of years ago. There are sections of time labeled “eons,” “eras,” and “periods.” Eons take up the longest time. Periods are the shortest. CASSIE: Like, you’ve probably heard of the Jurassic period. That’s a period in the geologic time scale that began 200 million years ago. An animation shows two brontosauruses by a lake. CASSIE: It gets its name from the Jura Mountains, where strata from that time were first studied. An image shows the Jura Mountains on a map in Switzerland. MOBY: Beep! Moby hands Cassie a slice of cake. CASSIE: Whoa, whoa, whoa--it's a layer cake record of my life? That's so cool! An animation shows small white pieces in the cake. CASSIE: Are those little candy fossils? MOBY: Beep. CASSIE: My baby teeth. Cassie sets the plate down. CASSIE: Eugh. Category:BrainPOP Science Transcripts Category:BrainPOP Transcripts